Tractor-trailer brake control system

ABSTRACT

A tractor-(28) trailer (30) vehicle (24) brake system control for distributing the brake effort to obtain inter-tractor-trailer proportional braking (H 1  /V 1  =H 2  /V 2 ) by use of sensors (170, 172) mounted to the trailer only is provided. The control system senses (80) acceleration (a) and the ratio of vertical to horizontal forces (H F  /V F ) at the fifth wheel (34) by sensors (170, 172) mounted to the tractor (28) only and modulates the brakes to cause the ratio H F  /V F  to equal acceleration.

BACKGROUND OF THE INVENTION

1. Related Applications

This application is related to Ser. No. 043,063, now U.S. Pat. No.4,768,840 and Ser. No. 043,010, both filed Apr. 17, 1987.

2. Field of the Invention

This invention relates to controls for brake systems for multiplevehicle systems (i.e. tractor - trailer vehicles). In particular, thisinvention relates to controls for vehicle brake systems which willdistribute the braking effort between the individually controllablevehicle brake sites, such as between sub-vehicle brake systems, toachieve inter-vehicle proportional braking.

3. Description of the Prior Art

Brake systems, and the controls therefor, for vehicles, including heavyduty vehicles such as trucks, are, of course, well known in the priorart.

Brake systems for passenger cars are, in general, somewhat easier todesign than brake systems for heavy duty vehicles such as trucks as theloading and maintenance of passenger vehicles will not vary to theextent loading and maintenance will vary in a truck, such as the loadingon the tractor of a tractor-trailer which may comprise a tractor only, atractor with an empty or lightly loaded trailer or a tractor with aheavily loaded trailer.

Brake systems of the anti-lock type, for all types of vehicles, are wellknown in the prior art. Briefly, these systems operate to obtain amaximized vehicle stability (i.e. maximized transverse coefficient offriction of braked wheels) by maintaining the longitudinal slip of thebraked wheels within predetermined limits. This usually requiresmodulating the braking forces on an individual wheel and/or individualaxle basis to maintain at least some wheel rotation.

Examples of prior art anti-lock systems may be seen by reference to U.S.Pat. Nos. 3,767,270; 3,768,872; 3,854,556; 3,893,696; 3,929,383;3,929,382; 3,966,267; 4,392,202 and 4,591,213, the disclosures of all ofwhich are hereby incorporated by reference.

Brake systems which control braking to achieve a driver demand, senseddriver demand in "brake-by-wire" manner, sense coefficient of frictionand modified brake forces accordingly, sense load on a wheel andmodified braking effort accordingly, sense wheel slip and/or usedelectronic signals to achieve more rapid trailer brake response are alsodisclosed in the prior art as may be seen by reference to U.S. Pat. Nos.4,140,352; 4,327,414; 4,494,199; 4,512,615; 4,545,240; 4,591,213;4,606,586; 4,616,881; and 4,648,663, the disclosures of which are herebyincorporated by reference.

While the prior art brake systems which modify braking effort inresponse to sensed parameters to achieve various goals, such as vehiclestability or the like, do, in general, provide enhanced vehicle braking,they are subject to further improvement. In the prior art systems fortractor-trailer vehicles, if braking effort between the tractor andtrailer is to be controlled in a predetermined manner, a speciallyconfigured and equipped trailer is required.

SUMMARY OF THE INVENTION

In accordance with the present invention, many of the drawbacks of theprior art have been overcome or minimized by the provision of a vehiclebrake control system particularly well suited for heavy duty articulatedmultiple vehicle systems such as tractor-trailers. The system providesthe advantages of improved performance as to both opening costs andsafety while being of a relatively lower cost than prior art brakesystems.

The above is accomplished by providing a brake control system havingmeans to sense the magnitude of the brake effort required by theoperator (usually sensed as a percentage of displacement of the vehiclebrake pedal) and means to distribute the braking effort between thebraked wheels, or sets of braked wheels, to achieve porportionedbraking.

When installed in a semi-truck tractor, the system preferably includessensors in the connecting apparatus (i.e. the fifth wheel) forconnecting the tractor to a selected trailer which will allowinter-tractor-trailer proportional braking without requiring specializedequipment on the trailer.

Accordingly, it is an object of the present invention to provide animproved vehicle braking system control for distributing the brakingeffort between the individually controllable subvehicle brake systems toachieve proportional braking.

This and other objectives and advantages of the present invention willbecome apparent from a reading of the detailed disclosure of thepreferred embodiments taken in connection with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a multiple vehicle system in whichthe brake control system of the present invention may be utilized.

FIG. 2 is a schematic illustration of a prior art load sensor which maybe utilized with the brake system of the present invention.

FIG. 3 is a schematic illustration of the brake system of the presentinvention for the multiple vehicle system of FIG. 1.

FIG. 4 is a schematic illustration of a standard trailer brake systemwhich may be utilized with the brake system of FIG. 2.

FIG. 5 is a force diagram for a braked wheel.

FIG. 6 is an equilibrium force diagram for the multiple vehicle systemof FIG. 1.

FIG. 7 is a schematic illustration of an alternate control device forthe brake control system of the present invention.

The vehicle brake control system of the present invention is effectiveto distribute the braking effort between the individually controlledbraked wheels or sets of wheels of the vehicle in multiple modes as afunction of the magnitude of operator demand for braking effort.

One of the modes, herein defined as the "proportional braking" mode, iswell known in the vehicle industry and involves the "braking ratio",which is the ratio of tangential friction force to radial load (i.e.F_(F) /F_(N) in FIG. 5) for the tire/road interface.

The limiting value, of course, is the coefficient of friction ("MU"). Ifeach wheel or set of wheels develops tangential friction force (orbraking force) to load in the same proportion, or ratio, then, to theextent each of the wheels have equal MU to slip relationships, thevehicle can utilize all of the available adhesion on all of its wheelsat the same time. This principal and the advantageous effects ofachieving equal braking ratios at each wheel is well known in thebraking industry.

Specifically proportional braking, as used herein means a braking effortdistribution on a vehicle where the ratio of tangential braking force toradial load force is (or very nearly is) the same for all wheels or setsof wheels. The wheels may be considered individually or taken in sets,the sets may consist of all of the wheels on one axle, all of the wheelson a tandem pair of axles (a bogey set), or all the wheels on onesub-vehicle when the vehicle is the combined total of severalsub-vehicles.

Another, different, principal for the distribution of braking effort ina vehicle braking system is to create braking energy inputs related tosome brake or vehicle system parameter other than the loads or tire toroad adhesion factors. Some of these parameters are: balanced wear, orbalanced work, or balanced temperature between brakes. Whatever theparameter chosen, the distribution of braking effort to balance it is,in general, different from the distribution of braking effort inproportional braking.

The braking system of the present invention, as it relates to a multiplevehicle system such as semi-truck tractor trailer system 24, involves atleast the inter-vehicle braking effort distribution between tractor 28and trailer 30, and may also involve the intra-vehicle braking effortdistribution for tractor 28 and the intra-vehicle braking effortdistribution for trailer 30.

The braking system of the present invention is applicable tomulti-vehicle systems such as the tractor 28 and trailer 30 system 24illustrated in FIG. 1. Referring to FIG. 3, the braking system for thetractor 28 of multi-vehicle system 24 may be seen. Briefly, as is wellknown in the prior art, tractor 28 includes a front steer axle 40, whichis usually not driven, and a tandem pair of rear drive axles comprisingfront-rear drive axle 36 and rear-rear drive axle 38. Wheels 140 and 142are associated with the rear-rear drive axle 38, wheels 144 and 146 areassociated with the front-rear drive axle 36 and wheels 148 and 150 areassociated with the front steer axle 40. As is typical with tractors,dual tires are utilized with each wheel of the rear drive axles.

The rear drive axles 36 and 38 are driven by engine 46 throughtransmission 48 and driveline 50. Air actuated brakes 60, 62, 152 and154 are provided for braking the rotation of wheels 144, 146, 140, 142,respectively, and air actuated brakes 64 and 66 are provided for brakingthe rotational speed of wheels 148 and 150, respectively. Rear brakes60, 62, 152 and 154 are, as is well known in the prior art, of the samesize and type as likewise are front brakes 64 and 66. In the systemillustrated, the brakes are air actuated brakes of one of the well knowntypes such as the "S" cam actuated drum brake type or the air disc braketype, the details of which are well known in the prior art and may beseen in greater detail by reference to U.S. Pat. Nos. 4,476,968 and4,457,407, the disclosures of both of which are hereby incorporated byreference. As is known, while both of the front brakes and all of therear brakes should be of the same size and type, it is not necessarythat the front brakes same size and/or type as the rear brakes.Compressed air for actuating the brakes is supplied from a plurality ofsupply tanks 68, only one of which is shown, from the vehicle compressor(not shown) or the like.

The braking system includes a control unit 70, which for purposes offlexibility and responsiveness is preferably an electronicmicroprocessor based control unit having means 72 for receiving aplurality of input signals, means for processing the input signals inaccordance with predetermined logic rules, and means 74 for issuingcommand output signals to various system operators.

A sensor 76 senses the operator's displacement of a brake pedal 78 toprovide an input signal indicative of the driver's demand for vehiclestopping effort. Sensors of this type are known in the prior art and maybe seen in greater detail by reference to U.S. Pat. Nos. 4,140,352;4,327,414 and 4,512,615. Typically, such transducers will sense thedisplacement of and/or force applied to the brake pedal 78 and willprovide an output signal proportional thereto. An input signalindicative of the deceleration of the vehicle may be provided by meansof a decelerometer 80 which is fixed to the vehicle or by means of atransmission output shaft speed sensor 82 which will provide a signalindicative of the rotational speed of the drive line which may bedifferentiated by the CPU 70. Force sensors 82, 84, 86, 88, 156 and 158are utilized to provide input signals indicative of the braking and loadforces at the wheels respectively. The force sensors may be strain gaugebased and/or of the linearly variable displacement transducer type as iswell known in the prior art. For purposes of achieving a more accuratedistribution of braking effort during a brake balancing mode,temperature sensors 90, 92, 94, 96, 164 and 166 may be provided forsensing the temperatures of the brakes at the wheels. The temperaturesensors may be non-contact infrared sensors, or the like, as is known inthe prior art. To allow the brake system to have an anti-lock mode,wheel speed sensors 98, 100, 102, 104, 106 and 162 are provided toprovide input signals indicative of the rotational speed of the wheels.

The central processing unit 70 will, as will be explained in greaterdetail below, process the input signals in accordance with predeterminedlogic rules to generate command output signals to the control valves 168and 175. Control valve 168 is connected to supply line 110 from one ofthe supply tanks and, in accordance with the command output signals,will independently pressurizes the conduits. A control valve 108 maybeutilized to independently control the braking at the front wheels 158and 150. Accordingly, it may be seen that the braking effort at each ofthe wheels may be individually controlled in a closed loop manner inresponse to command output signals generated by the CPU 70 in responseto the input signals received and processed thereby.

In a tractor-trailer vehicle system such as system 24 illustrated inFIG. 1, the inter-vehicle distribution of braking efforts is extremelyimportant. Generally speaking, in order of magnitude of importance toachieve acceptable vehicle brake performance from both the minimizedmaintenance and maximized braking peformance and stability goals,inter-tractor-trailer proportioned and balanced braking is at least asimportant as intra-tractor proportional and balanced braking and isconsidered to be more important than intra-trailer proportional andbalanced braking. Accordingly, in a braking system for atractor-trailer, it is important that means be provided to achieveinter-tractor-trailer braking effort distributions as discussed above.Further, it is also important to remember that tractors 28 are oftenowned by different individuals than those that own the trailers 30 and,even within a fleet with commonly owned tractors and trailers, a typicalfleet will have many many more trailers than tractors. Accordingly, itis highly desirable to provide a braking control system for atractor-trailer vehicle system which requires little if any specialequipment on the trailer and will provide relatively accuratetractor-trailer proportional braking and some degree ofinter-tractor-trailer balanced braking.

To achieve a tractor-trailer braking system which will provide anacceptable degree of inter-tractor-trailer proportional braking, whilerequiring no additional equipment on the trailer, the tractor of thepresent invention is equipped with an accelerometer 80 for providing aninput signal to CPU 70 indicative of the acceleration/deceleration ofthe vehicle and a pair of load sensors 170 and 172 for providing inputsignals to the CPU 70 indicative of the vertical and horizontal forcesat the fifth wheel connection 34 between the tractor and trailer. Inaddition, a control valve 174, controlled by command outputs from CPU70, will provide pilot or control signals to the standard trailer brakesystem control valves.

Referring now to FIG. 4, a prior art standard trailer brake system isillustrated. Briefly, the trailer includes a king pin 176 for selectiveengagement and disengagement to the tractor fifth wheel 34 as is wellknown in the prior art. The trailer includes a supply tank 178 connectedto the tractor air system by means of a fluid connection 180. Traileraxles 42 and 44 support trailer wheels 182, 184, 186 and 188, each ofwhich is provided with an air brake 190, 192, 194 and 196, respectively.Typically, all of the trailer brakes are controlled at the same pressureby means of a relay valve 198, which has an inlet 200 connected to thetrailer supply tank 178, and a pilot valve portion 202 for receiving apilot air signal from the tractor air system by means of connector 204.Connector 204 is designed for connection with connector 206 on thetractor. Typically, the connectors 204 and 206 and likewise connector180 and its associated connection with the vehicle air system (notshown) that form the fluid connection are known as the "glad hand".

As may be seen by reference to FIG. 4, the prior art standard trailer 30has a brake system wherein each of the brakes is actuated at the samepressure from a single output 208 from the pilot controlled relay valve198 and are thus all actuated at the same pressure which pressure is afunction of the pressure to the pilot valve portion 202. Accordingly, asall of the brakes 190, 192, 194 and 196 are actuated at the samepressure and as individual control of the actuating pressures thereof isnot available in a standard trailer, controlling the distribution of thebraking effort between the trailer brakes to achieve intra-trailerbalanced or proportional braking on a controlled basis is not possible.However, by utilizing the tractor braking system illustrated,inter-tractor-trailer proportional and, to a degree, balanced braking,is obtainable.

As may be seen from the equilibrium force diagrams of FIG. 6, which donot include the aerodynamic, grade or transient forces:

    H.sub.1 =-M,a+H.sub.F

    V.sub.2 =M.sub.1 g+V.sub.F

    H.sub.2 =-M.sub.2 a-H.sub.F

    V.sub.2 =M.sub.2 g-V.sub.F

where M₁ =mass of tractor 20

M₂ =mass of trailer 30

H₁ =braking force of tractor 28;

H₂ =braking force of trailer 30;

H_(F) =horizontal force at fifth wheel 34/ king pin 178;

V₁ =weight supported by tractor axles;

V₂ =weight supported by trailer axles;

V_(F) =weight on fifth wheel;

g=gravity

a=forward acceleration.

At tractor-trailer proportional braking conditions, the braking ratio ofthe tractor (taken as a unit) will be equal to the braking ratio of thetrailer (taken as a unit), or;

    H.sub.1 /V.sub.1 =H.sub.2 /V.sub.2

Additionally, the braking ratio of the interconnecting assembly (H_(F)/V_(F)) will equal the same value, i.e.:

    H.sub.F /V.sub.F =H.sub.2 /V.sub.2 =H.sub.1 /V.sub.1

Given the above relationship is, it may be seen that, if H_(F) /V_(F)=-a, then tractor-trailer proportional braking is achieved. Accordingly,by modulating the pressure applied to the tractor brakes (control ofvalves 108 and 168) and/or to the trailer brakes (control of valve 174),to minimize the error equation:

    E=H.sub.F /V.sub.F *C+A

tractor-trailer proportional braking, regardless of the load on thetrailer, is provided and requires no additional sensors and/or controldevices on the trailer.

Vehicle acceleration/deceleration can also be measured by use of thewheel speed sensors if proper allowance is made for slip. Of course, byusing the vehicle acceleration/deceleration measurement device 80 incombination with the wheel speed sensors, a very accurate determinationof wheel slip may be calculated.

An alternate, totally mechanical system, attached solely to the tractor28, for maintaining tractor-trailer proportional braking by modulatingair pressure to the trailer brakes to minimize the equation:

    E=H.sub.F /V.sub.F *C+A

is illustrated in FIG. 7.

The fifth wheel 34 is mounted to the tractor 28 by a fifth wheelcarriage 300 pivotably supported by a pair of links 302. A mass 304 ispivotably mounted to the tractor 28 by a link 306. A valve 308 forcontrolling the supply of air to the trailer axle brakes is mounted tothe fifth wheel carriage and is controlled by a horizontally extendingvalve plunger 310 fixed to link 306 for horizontal movement therewith.Valve 308 will replace the valve 174 illustrated in FIG. 6.

Links 302 define an angle 320 relative to vertical while link 306defines an angle 330 relative to vertical. Briefly, the tangent of angle330 is proportional to vehicle deceleration a while the tangent of angle320 is proportional to the ratio V_(F) /H_(F). Thus, if properly sized,at tractor-trailer proportional braking, (i.e. when H_(F) /V_(F) =a),the tangent of angle 330 will equal the tangent of angle 320.

When the tractor brakes are applied with greater braking ratio than thetrailer brakes, both the mass 304 and the fifth wheel carriage 300 willswing forward with angle 320 being greater than angle 330. This willcause valve plunger 310 to increasingly extend into the valve 308 toincrease the pilot air pressure in line 206 to the trailer control valvepilot port 202. If the trailer brake ratio is greater than the tractorbrake ratio, angle 330 will be greater than angle 320 and plunger 310will decreasingly extend into control valve 308 to decrease the pilotpressure supplied to pilot air conduit 206.

A braking system for a multi-vehicle system, such as a tractor-trailersemi-truck 24 is provided that allows the inter-tractor-trailer brakingeffort to be distributed in a manner to achieve inter-tractor-trailerproportional braking while utilizing special sensors and control locatedsolely on the tractor.

While the preferred embodiments of the present invention have beendescribed in connection with specific apparatus, the descriptions aremade by way of example only and not as limitations on the spirit andscope of the invention as hereinafter claimed.

I claim:
 1. A method for controlling the brake system on atractor-trailer vehicle having a fifth wheel/king pin connectingstructure and individually controllable tractor and trailer sub-vehiclebrake system, said method characterized by:(a) sensing .[.from alocation on said trailer sub-vehicle.]. the value of a parameterindicative of the vertical force exerted on the fifth wheel kingpin/connection; (b) sensing .[.from a location on said trailersub-vehicle.]. the value of a parameter indicative of the horizontalforce exerted by the king pin on the fifth wheel; (c) sensing .[.from alocation on said trailer sub-vehicle.]. the value of a parameterindicative of the acceleration of the vehicle; (d) modulating thebraking forces exerted by .Iadd.at least one of .Iaddend.the.Iadd.tractor and .Iaddend.trailer sub-vehicle brake .[.system only.]..Iadd.systems .Iaddend.to minimize the value of the expression:

    E=a function of .[.(H.sub.F /V.sub.F)+a.]. (.Iadd.H.sub.F -V.sub.F *a) .Iaddend.

where: E=error; H_(F) =horizontal force at the fifth wheel/king pinconnection; V_(F) =vertical force imposed at the fifth wheel/king pinconnection; and a=forward acceleration of vehicle (expressed in units ofgravity).
 2. The method of claim 1 wherein the steps of (a) and (b)comprise sensing the value of a parameter indicative of the value of theratio:

    H.sub.F /V.sub.F (in units of gravity).


3. .[.A control system for a tractor-trailer brake system on atractor-trailer vehicle having an independently controllable tractorsub-vehicle brake system, a fifth wheel connection for engaging a kingpin carried by a trailer sub-vehicle and an individually controllabletrailer sub-vehicle brake system, said control system characterizedby:first sensing means mounted on said trailer sub-vehicle for providingan input signal indicative of the value of the ratio of the horizontalforce to the vertical force at the fifth wheel/king pin connection,second sensing means mounted on said trailer sub-vehicle for providingan input signal indicative of the acceleration of the vehicle; a controlunit mounted on said trailer sub-vehicle having means for receiving saidinput signals and for processing said signals in accordance withpredetermined logic rules to issue command output signals and actuatorsresponsive to said command output signals for modulating a controlledparameter at the trailer sub-vehicle brake system related to the brakeforce at the trailer sub-vehicle brake system; said control unitincluding means for modulating the braking forces at said trailersub-vehicle brake system only to minimize the value of the expression;

    E=a function of (H.sub.F +(V.sub.F *a))

.]. .Iadd.A method for controlling the brake system on a tractor-trailervehicle having a tractor with a fifth wheel for connection with atrailer king pin, an individually controllable tractor sub-vehicle brakesystem and an individually controllable trailer sub-vehicle brakesystem, said method comprising the steps of: sensing the value of aparameter indicative of the value H_(F) /V_(F), sensing the value ofvehicle acceleration (a), sensing the value of operator demand forvehicle braking (D), and modulating the braking forces exerted by thesub-vehicle brake systems to minimize the value of the expression:

    E=a function of (H.sub.F -V.sub.F *a)

.Iaddend. where: E=error; H_(F) =horizontal force at fifth wheel/kingpin connection; V_(F) =vertical force imposed at the fifth wheel/kingpin connection; and a=forward acceleration of vehicle (expressed inunits of gravity).
 4. A brake control system for a tractor-trailer brakesystem on a tractor-trailer vehicle having a tractor sub-vehicleequipped with an independently controllable tractor sub-vehicle brakesystem, a fifth wheel connection for engaging a king pin carried by atrailer sub-vehicle and a master control for controlling an individuallycontrollable trailer sub-vehicle brake system, said control systemcharacterized by:first sensing means for providing an input signalindicative of the value of the ratio of the horizontal force to thevertical force at the fifth wheel/king pin connection, second sensingmeans for providing an input signal indicative of the acceleration ofthe vehicle; a control unit having means for receiving said inputsignals and for processing said signals in accordance with predeterminedlogic rules to issue command output signals and actuators responsive tosaid command output signals for modulating a controlled parameter ateach sub-vehicle brake system related to the brake force at thesub-vehicle brake system; said control unit including means formodulating the braking forces .Iadd.of .Iaddend.at least one of saidsub-vehicle brake systems to minimize the value of the expression;

    E=a function of (H.sub.F -V.sub.F *a)

where: E=error; H_(F) =horizontal force at the fifth wheel/king pinconnection; V_(F) =vertical force imposed at the fifth wheel/king pinconnection; and a=forward acceleration of the vehicle (in units ofgravity).
 5. The control system of claim 4 wherein said first sensingmeans is mounted on said tractor sub-vehicle.
 6. The control system ofclaim 5 wherein said first sensing means comprises transducers attachedto said fifth wheel.
 7. A brake control system for a tractor-trailerbrake system on a tractor-trailer vehicle having a tractor sub-vehicleequipped with an independently controllable tractor sub-vehicle brakesystem, a fifth wheel connection for engaging a king pin carried by atrailer sub-vehicle and a master control for controlling an individuallycontrollable trailer sub-vehicle brake system, said control systemcharacterized by:first sensing means for providing an input signalindicative of one of (i) the value of parameters indicative of thehorizontal and vertical forces exerted on the fifth wheel/king pinconnection and ii) the value of the ratio of the horizontal force to thevertical force at the fifth wheel/king pin connection, second sensingmeans for providing an input signal indicative of the acceleration ofthe vehicle; a control unit having means for receiving said inputsignals and for processing said signals in accordance with predeterminedlogic rules to issue command output signals and actuators responsive tosaid command output signals for modulating a controlled parameter ateach sub-vehicle brake system related to the brake force at thesub-vehicle brake system; said control unit including means formodulating the braking forces at at least one of said sub-vehicle brakesystems to minimize the value of the expression E where E is a functionof H_(F), V_(F) and a; where: E=error; H_(F) =horizontal force at thefifth wheel/king pin connection; V_(F) =vertical force imposed at thefifth wheel/king pin connection; and, a=forward acceleration of thevehicle.